Dc-dc converter and organic light emitting display including the same

ABSTRACT

Disclosed are a direct current converter and an organic light emitting display including the converter. The converter includes a power supply generating an input power, a first power generator receiving the input power and a selected voltage from a selector and generating a first voltage, a first output terminal connected to the first power generator and outputting the first voltage; a second power generator receiving the input power and generating a second voltage, a second output terminal connected to the second power generator and outputting the second voltage, an external feedback wiring providing a feedback voltage, a feedback terminal connected to the external feedback wiring and inputting the feedback voltage to the selector, and the selector connected to and transferring the selected voltage to the first power generator, where the selected voltage is one of the feedback voltage and the voltage output from the first output terminal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean PatentApplication No. 10-2012-0022840, filed on Mar. 6, 2012, in the KoreanIntellectual Property Office, the entire content of which isincorporated herein by reference.

BACKGROUND

1. Field

The present disclosure relates to a direct current (DC)-DC converter andan organic light emitting display including the same, in which the DC-DCconverter is capable of being normally operated without additionaldamage if a feedback wiring present at an outer portion thereof isdisconnected.

2. Description of the Related Technology

Recently, various displays capable of reducing weight and volume, whichare disadvantages of a cathode ray tube, have been developed. Asexamples of these displays, there are liquid crystal display (LCD), afield emission display (FED), a plasma display panel (PDP), an organiclight emitting display (OLED), and the like.

Among them, the organic light emitting display, which displays an imageusing an organic light emitting diode generating light by recombinationbetween electrons and holes, has advantages including a rapid responsespeed and being driven at low power.

The OLED is configured to include a display module including a scandriver, a data driver, and a pixel unit to display a screen; and adirect current (DC)-DC converter supplying power to the display module.

The DC-DC converter generates power required for driving the pixel unitby converting external power. The DC-DC converter may receive outputvoltage fed back through a feedback wiring present at an outer portionof the DC-DC converter in order to appropriately adjust output powervoltage.

That is, the DC-DC converter may be operated in a scheme of increasingthe output power voltage when the fed back voltage is low, anddecreasing the output power voltage when the fed back voltage is high.

However, if the feedback wiring is disconnected due to impact or thelike, the fed back voltage rapidly decreases, and the DC-DC convertercontinuously increases the output power voltage correspondingly.

Therefore, power voltage exceeding an allowable range is supplied tocircuits configuring the display module, thereby potentially causing todamage the circuits.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

An object of the present invention is to provide a direct current(DC)-DC converter which can be normally operated without an additionaldamage if a feedback wiring present at an outer portion thereof isdisconnected. Embodiments disclosed herein also include an organic lightemitting display including the DC-DC converter.

According to one embodiment, there is provided a direct current DC-DCconverter, including: a power supply generating an input power, a firstpower generator receiving the input power and a selected voltage from aselector and generating a first voltage, a first output terminalconnected to the first power generator and outputting the first voltage;a second power generator receiving the input power and generating asecond voltage, a second output terminal connected to the second powergenerator and outputting the second voltage, an external feedback wiringproviding a feedback voltage, a feedback terminal connected to theexternal feedback wiring and inputting the feedback voltage to theselector, and the selector connected to and transferring the selectedvoltage to the first power generator, where the selected voltage is oneof the feedback voltage and the voltage output from the first outputterminal.

The selector may include: a switching unit including a first and asecond switching device transferring the selected voltage to the firstpower generator, where the first switching device may transfer thevoltage output from the first output terminal and the second switchingdevice may transfer the feedback voltage input from the feedbackterminal; and a controller controlling the alternate turn-ons of thefirst switching device and the second switching device.

The controller may include a comparator comparing the feedback voltagewith a preset reference voltage to determine which of the first andsecond switching devices to turn on. The second switching device may beturned on if the feedback voltage is larger than the preset referencevoltage, and the first switching device may be turned on if the feedbackvoltage is smaller than the preset reference voltage.

The first switching device and the second switching device may beimplemented as a transistor, and the controller may include: a firstinverter having an input terminal connected to the feedback terminal andan output terminal connected to an input terminal of a second inverterand a gate electrode of the second switching device; and the secondinverter having an input terminal connected to the output terminal ofthe first inverter and an output terminal connected to a gate electrodeof the first switching device.

The first power generator may include: a first inductor connectedbetween the power supply unit and a first node; a first transistorconnected between the first node and a ground power supply; a secondtransistor connected between the first node and the first outputterminal; a first switching controller controlling the first transistorand the second transistor; and a first voltage divider dividing voltagesupplied from the selector to supply the divided voltage to theswitching controller.

The first voltage divider may include a plurality of resistors connectedin series with each other.

The second power generator may include: a third transistor connectedbetween the power supply unit and a second node; a fourth transistorconnected the second node and the second output terminal; a secondinductor connected between the second node and a ground power supply; asecond switching controller controlling the third transistor and thefourth transistor; and a second voltage divider dividing voltage at theoutput terminal to supply the divided voltage to the second switchingcontroller.

The second voltage divider may include a plurality of resistorsconnected in series with each other.

The first voltage may have a positive polarity, and the second voltagemay have a negative polarity.

According to another embodiment, there is provided an organic lightemitting display including: a plurality of pixels connected to scanlines, data lines, a first power line and a second power line; and aDC-DC converter generating a first voltage and a second voltage torespectively supply to the pixels through the first power line and thesecond power line, wherein the DC-DC converter includes: a power supplygenerating an input power, a first power generator receiving the inputpower and a selected voltage from a selector and generating a firstvoltage, a first output terminal connected to the first power generatorand outputting the first voltage; a second power generator receiving theinput power and generating a second voltage, a second output terminalconnected to the second power generator and outputting the secondvoltage, an external feedback wiring providing a feedback voltage, afeedback terminal connected to the external feedback wiring andinputting the feedback voltage to the selector, and the selectorconnected to and transferring the selected voltage to the first powergenerator, where the selected voltage is one of the feedback voltage andthe voltage output from the first output terminal.

The selector may include: a first and a second switching devicetransferring the selected voltage to the first power generator, wherethe first switching device may transfer the voltage output from thefirst output terminal and the second switching device may transfer thefeedback voltage input from the feedback terminal; and a controllercontrolling the alternate turn-ons of the first switching device and thesecond switching device.

The controller may include a comparator comparing the feedback voltagewith a preset reference voltage to determine which of the first andsecond switching devices to turn on. The second switching device may beturned on if the feedback voltage is larger than the preset referencevoltage, and the first switching device may be turned on if the feedbackvoltage is smaller than the preset reference voltage.

The first switching device and the second switching device may beimplemented as a transistor, and the controller may include: a firstinverter having an input terminal connected to the feedback terminal andan output terminal connected to an input terminal of a second inverterand a gate electrode of the second switching device; and the secondinverter having an input terminal connected to the output terminal ofthe first inverter and an output terminal connected to a gate electrodeof the first switching device.

The first power generator may include: a first inductor connectedbetween the power supply unit and a first node; a first transistorconnected between the first node and a ground power supply; a secondtransistor connected between the first node and the first outputterminal; a first switching controller controlling the first transistorand the second transistor; and a first voltage divider dividing voltagesupplied from the selector to supply the divided voltage to theswitching controller.

The first voltage divider may include a plurality of resistors connectedin series with each other.

The second power generator may include: a third transistor connectedbetween the power supply unit and a second node; a fourth transistorconnected the second node and the second output terminal; a secondinductor connected between the second node and a ground power supply; asecond switching controller controlling the third transistor and thefourth transistor; and a second voltage divider dividing voltage at theoutput terminal to supply the divided voltage to the second switchingcontroller.

The second voltage divider may include a plurality of resistorsconnected in series with each other.

The first voltage may have a positive polarity, and the second voltagemay have a negative polarity.

The organic light emitting display according to the present inventionmay further include a scan driver supplying scan signals to pixelsthrough the scan lines; and a data driver supplying data signals topixels through the data line.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, together with the specification, illustratecertain embodiments of the present invention, and, together with thedescription, serve to explain the principles of the present invention.

FIG. 1 is a view showing an embodiment of an organic light emittingdisplay;

FIG. 2 is a view showing a pixel shown in FIG. 1;

FIG. 3 is a view showing an embodiment of a direct current DC-DCconverter;

FIG. 4 is a view showing a detailed configuration of the embodiment of aDC-DC converter shown in FIG. 3;

FIG. 5 is a view showing an embodiment of a selector; and

FIG. 6 is a view showing another embodiment of a selector.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

In the following detailed description, only certain embodiments of thepresent invention have been shown and described, simply by way ofillustration. As those skilled in the art would realize, the describedembodiments may be modified in various ways, without departing from thespirit or scope of the present invention. Accordingly, the drawings anddescription are to be regarded as illustrative in nature and notrestrictive. In addition, when an element is referred to as being “on”another element, it can be directly on the other element or beindirectly on the other element with one or more intervening elementsinterposed therebetween. Also, when an element is referred to as being“connected to” another element, it can be directly connected to theother element or be indirectly connected to the other element with oneor more intervening elements interposed therebetween. Hereinafter, likereference numerals generally refer to like elements.

Advantages and features of the present invention and methods to achievethem will be elucidated from certain embodiments described below indetail with reference to the accompanying drawings. However, the presentinvention is not limited to embodiments disclosed below, but may beimplemented in various different forms.

FIG. 1 is a view showing an embodiment of an organic light emittingdisplay.

Referring to FIG. 1, an embodiment of the organic light emitting displaymay include: a pixel unit 20 including pixels 10 each connected to scanlines Si through Sn, data lines D1 through Dm, a first power line 81,and a second power line 82; a scan driver 30 supplying scan signals toeach pixel 10 through the scan lines S1 through Sn; a data driver 40supplying data signals to each pixel 10 through the data lines D1through Dm; and a DC-DC converter 60 supplying first power ELVDD andsecond power ELVSS to each pixel 10 through the first power line 81 andthe second power line 82. In addition, the organic light emittingdisplay may further include a timing controller 50 for controlling thescan driver 30 and the data driver 40. Each of the pixels 10 receivingthe first power ELVDD and the second power ELVSS from the DC-DCconverter 60 through the first power line 81 and the second power line82 generates light corresponding to the data signal by current flowingfrom a first power supply ELVDD to a second power supply ELVSS via theorganic light emitting diode.

The scan driver 30 generates the scan signals by a control of the timingcontroller 50 and supplies the generated scan signals to the scan linesS1 through Sn.

The data driver 40 generates the data signals by a control of the timingcontroller 50 and supplies the generated data signals to the data linesD1 through Dm.

When the scan signals are sequentially supplied to the scan lines S1through Sn, the pixels 10 are sequentially selected for each line andthe selected pixels 10 receive the data signals transferred from thedata lines D1 through Dm.

FIG. 2 is a view showing a pixel shown in FIG. 1. Particularly, forconvenience of explanation, a pixel connected to an n-th scan line Snand an m-th data line Dm is shown in FIG. 2.

Referring to FIG. 2, each pixel 10 may include an organic light emittingdiode (OLED) and a pixel circuit 12 connected to the data line Dm andthe scan line Sn to control the OLED.

An anode electrode of the OLED is connected to the pixel circuit 12, anda cathode electrode thereof is connected to the second power supplyELVSS.

The OLED generates light having a predetermined brightness correspondingto current supplied from the pixel circuit 12.

The pixel circuit 12 may control an amount of current supplied to theOLED, corresponding to the data signal supplied to the data line Dm whenthe scan signal is supplied to the scan line Sn. To this end, the pixelcircuit 12 includes a second transistor T2 connected between the firstpower supply ELVDD and the OLED, a first transistor T1 connected betweenthe second transistor T2, and the data line Dm and the scan line Sn, anda storage capacitor Cst connected between a gate electrode and a firstelectrode of the second transistor T2.

The gate electrode of the first transistor T1 is connected to the scanline Sn, and the first electrode thereof is connected to the data lineDm. In addition, a second electrode of the first transistor T1 isconnected to one side terminal of the storage capacitor Cst. The firstelectrode is set to one of a source electrode and a drain electrode, andthe second electrode is set to the other of the source electrode and thedrain electrode. For example, when the first electrode is set to thesource electrode, the second electrode is set to the drain electrode.

The first transistor T1 connected to the scan line Sn and the data lineDm is turned-on when the scan signal is supplied from the scan line Sn,thereby supplying the data signal supplied from the data line Dm to thestorage capacitor Cst. The storage capacitor Cst is charged with voltagecorresponding to the data signal.

The gate electrode of the second transistor T2 is connected to one sideterminal of the storage capacitor Cst, and the first electrode thereofis connected to the other side terminal of the storage capacitor Cst andthe first power supply ELVDD. In addition, the second electrode of thesecond transistor T2 is connected to an anode electrode of the OLED.

The second transistor T2 controls an amount of current flowing from thefirst power supply ELVDD to the second power supply ELVSS via the OLED,corresponding to a voltage value stored in the storage capacitor Cst.The OLED generates light corresponding to the amount of current suppliedfrom the second transistor T2.

The pixel structure in FIG. 2 described above is only an example of thepresent invention. Therefore the pixel 10 according to the presentinvention is not limited to having the above-mentioned pixel structure.The pixel circuit 12 has a circuit structure capable of supplyingcurrent to the OLED, and may be selected to have any one of currentlyknown various structures.

The DC-DC converter 60 receives input power Vin from a power source unit70 and converts the input power Vin, to generate the first power ELVDDand the second power ELVSS supplied to each pixel 10.

The first power ELVDD may be set to having a positive polarity, and thesecond power ELVSS may be set to having a negative polarity.

The power source unit 70 may be a battery providing DC power to an inputterminal IN of the DC-DC converter 60 or a rectifying apparatusconverting alternating current (AC) power to DC power, but is notlimited thereto.

FIG. 3 is a view showing an embodiment of a DC-DC converter.

Referring to FIG. 3, an embodiment of the DC-DC converter 60 includes afirst power generator 110, a second power generator 120 and a selector130.

The first power generator 110 receives the input power Vin supplied fromthe power source unit 70 to generate the first power ELVDD, and outputsthe first power ELVDD to a first output terminal OUT1.

The first power ELVDD output to the first output terminal OUT1 of thefirst power generator 110 is supplied to each pixel 10 through the firstpower line 81.

The first power generator 110 may boost the input power Vin usinginternal devices to generate the first power ELVDD.

In addition, the first power generator 110, which may be a boost typeconverter boosting the input power Vin, may generate the first powerELVDD with the voltage having the positive polarity.

The second power generator 120 receives the input power Vin suppliedfrom the power source unit 70 to generate the second power ELVSS, andoutputs the second power ELVSS to a second output terminal OUT2.

The second power ELVSS output to the second output terminal OUT2 of thesecond power generator 120 is supplied to each pixel 10 through thesecond power line 82.

The second power generator 120 bucks the input power Vin using internaldevices to generate the second power ELVSS.

In addition, the second power generator 120, which is a buck-typeconverter bucking the input power Vin, may generate the second powerELVSS with the voltage having the negative polarity.

The selector 130 selectively transfers any one of feedback voltage Vfbpinput from the external feedback wiring 140 to a feedback terminal FBPand voltage Vout1 at the first output terminal OUT1 to the first powergenerator 110.

The first power generator 110 may appropriately adjust a voltage levelof the first power supply ELVDD by using the voltage Vfbp fed back bythe selector 130 or the voltage Vout1 at the first output terminal OUT1.

The feedback wiring 140 may be electrically connected to the first powerline 81 present at the outer portion of the DC-DC converter 60, therebyinputting the voltage of the first power line 81 to the feedbackterminal FBP of the DC-DC converter 60. Further, the feedback wiring 140may be electrically connected to the first power line 81 present in thepixel unit 20.

A voltage drop occurs between the first output terminal OUT1 and thepower line 81 connected to the pixels 10, such that a voltage differenceis actually present between the voltage Vout1 at the first outputterminal OUT1 and the voltage of the first power ELVDD supplied to thepixels 10.

In the case in which the DC-DC converter 60 is connected to the pixels10 through a flexible printed circuit board (FPCB) at the outer portionof the display module configured of the pixel unit 20, the scan driver30 and the data driver 40, the above-mentioned voltage differencelargely increases.

Therefore, in order to more accurately control the first power generator110, there is a need to feed back the voltage actually used in thedisplay module, instead of the voltage Vout1 at the first outputterminal OUT1.

Accordingly, the feedback wiring 140 electrically connected to the firstpower line 81 present in the display module is provided and the selector130 is also provided in the DC-DC converter 60, thereby making itpossible to selectively supply any one of the voltage Vout1 at the firstoutput terminal OUT1 and the feedback voltage Vfbp to the first powergenerator 110.

In the case in which the feedback wiring 140 at the outer portion of theDC-DC converter 60 is disconnected due to impact, or the like, thefeedback voltage rapidly decreases, such that the first power generator110 continuously increases the voltage of the first power ELVDD outputto the first output terminal OUT1. Therefore, a circuit, or the like,configuring the OLED may be damaged.

In embodiments disclosed herein, in the case in which the feedbackvoltage Vfbp decreases due a problem such as disconnection, or the like,of the feedback wiring 140, the selector 130 may supply the voltageVout1 at the first output OUT1 rather than the feedback voltage Vfbp tothe first power generator 110.

Further, as needed, a user, a manufacturer, or the like, that is to useonly the voltage Vout1 at the first output terminal OUT1 does notintentionally install the feedback wiring 140 or disconnects aninstalled feedback wiring 140, thereby making it possible to use onlythe voltage Vout1 at the first output terminal.

FIG. 4 is a view showing a detailed configuration of the DC-DC convertershown in FIG. 3.

Referring to FIG. 4, an embodiment of the selector 130 may include acontroller 210 and a switching unit 220.

The switching unit 220 includes a first switching device 231 and asecond switching device 232 to selectively transfer any one of thefeedback voltage Vfbp and the voltage Vout1 at the first output terminalOUT1 to the first power generator 110.

The first switching device 231 is connected between the first powergenerator 110 and the first output terminal OUT1, thereby making itpossible to transfer the voltage Vout1 at the first output terminal OUT1to the first power generator at the time of turn-on thereof.

The second switching device 232 is connected between the first powergenerator 110 and the feedback terminal FBP, thereby making it possibleto transfer the feedback voltage Vfbp input to the feedback terminal FBOto the first power generator 110 at the time of turn-on thereof.

In order to selectively feed back any one of the feedback voltage Vfbpand the voltage at the first output terminal OUT1 to the first powergenerator 110, the first switching device 231 and the second switchingdevice 232 need to be alternately turned on.

Therefore, the controller 210 controls the first switching device 231and the second switching device 232 so as to be alternately turned on.

That is, the first output terminal OUT1 may be transferred to the firstpower generator 110 by turning on the first switching device 231 andturning off the second switching device 232.

In addition, the feedback voltage Vfbp may be transferred to the firstpower generator 110 by turning off the first switching device 231 andturning on the second switching device 232.

In some embodiments, the first and second switching devices 231 and 232constituting the switching unit 220 may be implemented as a transistor.

Referring to FIG. 4, the first power generator 110 may include a firstinductor L1, a first transistor M1, a second transistor M2, a firstswitching controller 310 and a first voltage divider 320.

The first inductor L1 is connected between the power source unit 70 anda first node N1.

The first transistor M1 is connected between the first node N1 and aground power supply.

The second transistor M2 is connected between the first node N1 and thefirst output terminal OUT1.

The first switching controller 310 controls the first transistor M1 andthe second transistor M2. In addition, the first switching controller310 controls turn-on/off operations of the first transistor M1 and thesecond transistor M2, thereby making it possible to convert the inputvoltage Vin into the first power ELVDD having a desired voltage level.

The first voltage divider 320 divides the voltage (the voltage Vout1 atthe first output terminal Out1 or the feedback voltage Vfbp) suppliedfrom the selector 130 to supply the divided voltage to the firstswitching controller 310.

More specifically, the first voltage divider 320 may receive the voltageVout1 at the first output terminal OUT1 or the feedback voltage Vfbpthrough the switching unit 220 included in the selector 130.

The first voltage divider 320 may be configured as a plurality ofresistors (for example R1 and R2) connected in series with each other.

The first switching controller 310 receiving the voltage divided by thefirst voltage divider 320 adjusts duty ratios of the first transistor M1and the second transistor M2, corresponding to the divided voltage,thereby making it possible to generate a desired first power ELVDD.

The first transistor M1 and the second transistor M2 may be alternatelyturned on. Therefore the first transistor M1 and the second transistorM2 may be of different conductive types. For example, when the firsttransistor is a P-type transistor, the second transistor M2 may be anN-type transistor.

Referring to FIG. 4, the second power generator 120 may include a secondinductor L2, a third transistor M3, a fourth transistor M4, a secondswitching controller 330 and a second voltage divider 340.

The second transistor M3 is connected between the power source unit 70and a second node N2.

The fourth transistor M4 is connected between the second node N2 and asecond output terminal OUT2.

The second inductor L2 is connected between the second node N2 and theground power supply.

The second switching controller 330 controls the third transistor M3 andthe fourth transistor M4. In addition, the second switching controller340 controls turn-on/off operations of the second transistor M3 and thefourth transistor M4, thereby making it possible to convert the inputvoltage Vin into the second power ELVSS having a desired voltage level.

The second voltage divider 340 divides the voltage Vout2 transferredfrom the second output terminal OUT2 to supply the divided voltage tothe second switching controller 330.

The second voltage divider 340 may be configured as a plurality ofresistors (for example R3 and R4) connected in series with each other.

The second switching controller 330 receiving the voltage divided by thesecond voltage divider 340 adjusts duty ratios of the third transistorM3 and the fourth transistor M4, corresponding to the divided voltage,thereby making it possible to generate a desired second power ELVSS.

The third transistor M3 and the fourth transistor M4 may be alternatelyturned on. Therefore, the third transistor M3 and the fourth transistorM4 may be of different conductive types. For example, when the thirdtransistor is an N-type transistor, the fourth

transistor M4 may be a P-type transistor. The configurations of thefirst power generator 110 and the second power generator 120 describedabove are only an example implementing the present invention. Therefore,the present invention is not limited thereto.

FIG. 5 is a view showing an embodiment selector.

Referring to FIG. 5, in an embodiment of the selector, the controller210 may include a comparator 240.

The comparator 240 receives the feedback voltage Vfbp input to thefeedback terminal FBP and a preset reference voltage Vref, and comparesmagnitudes of both voltages with each other.

The comparator 240 turns off the first switching device 231 and turns onthe second switching device 232 in the case in which the feedbackvoltage Vfbp is larger than the reference voltage Vref, and turns on thefirst switching device 231 and turns off the second switching device 232in the case in which the feedback voltage Vfbp is smaller than thereference voltage Vref.

As shown in FIG. 5, in the case in which the first switching device 231is implemented as a PMOS transistor and the second switching device 232is implemented as an NMOS transistor by way of example, an outputterminal of the comparator 231 may be connected to gate electrodes ofthe first switching device 231 and the second switching device 232.

Therefore, in the case in which the feedback voltage Vfbp is larger thanthe reference voltage Vref, when the comparator 240 outputs high-levelvoltage to the output terminal thereof, the first switching device 231may be turned off, and the second switching device 232 may be turned on.

Therefore, the feedback voltage Vfbp may be transferred to the firstpower generator 110 through the second switching device 232. Morespecifically, the feedback voltage Vfbp may be transferred to the firstvoltage divider 320 of the first power generator 110 through the secondswitching device 232.

In addition, in the case in which the feedback voltage is smaller thanthe reference voltage Vref, when the comparator 240 outputs low-levelvoltage to the output terminal thereof, the first switching device 231may be turned on and the second switching device 232 may be turned off.

Therefore, the voltage Vout1 at the first output terminal OUT1 may betransferred to the first power generator 110 through the first switchingdevice 231. More specifically, the voltage Vout1 at the first outputterminal OUT1 may be transferred to the first voltage divider 320 of thefirst power generator 110 through the first switching device 231.

When the comparator 240 is set to output the low-level voltage in thecase in which the feedback voltage Vfbp is larger than the referencevoltage Vref and to output the high-level voltage in the case in whichthe feedback voltage Vfbp is smaller than the reference voltage Vref,the first switching device 231 may be implemented as an NMOS transistorand the second switching device 232 may be implemented as a PMOStransistor.

Through the configuration as described above, an embodiment of theselector 130 supplies the voltage Vout1 at the first output terminalOUT1 rather than the feedback voltage Vfbp to the power generator 110 inthe case in which the feedback voltage Vfbp becomes lower than a presetreference voltage Vref due to a problem such as disconnection, or thelike, of the feedback wiring 140, thereby making it possible to normallyoperate the OLED without an additionally damage.

In addition, the controller 210 may further include a pull-down resistorR positioned between a common node between the feedback terminal FBP andthe comparator 240, and the ground power supply.

FIG. 6 is a view showing another embodiment of a selector.

Referring to FIG. 6, in another embodiment of the selector 130′, acontroller 210′ may include a first inverter 250 and a second inverter260.

In addition, first and second switching devices 231′ and 232′ includedin the switching unit 220′ may be implemented as transistors.

The first inverter 250 has an input terminal connected to a feedbackterminal FBP and an output terminal connected to an input terminal ofthe second inverter 260 and a gate electrode of the second switchingdevice 232′ implemented as the transistor.

The second inverter 260 has the input terminal connected to the outputterminal of the first inverter 250 and an output terminal connected to agate electrode of the first switching device 231′ implemented as thetransistor.

In addition, the controller 210′ may further include a pull-downtransistor 270 positioned between a common node between the inputterminal of the first inverter 250 and the feedback terminal FBP, andthe ground power supply. The pull-down transistor may be controlled tobe turned on/off by having a gate electrode connected to the outputterminal of the inverter 250.

In the case in which normal feedback voltage Vfbp is input to thefeedback terminal FBP, the first inverter 250 outputs low level voltagegenerated by inverting the feedback voltage Vfbp to the output terminal.

Accordingly, the second switching device 232′ of which the gateelectrode is applied with the low-level voltage is turned on. Therefore,the feedback voltage Vfbp may be transferred to the first powergenerator 110 through the second switching device 232′. Morespecifically, the feedback voltage Vfbp may be transferred to the firstvoltage divider 320 of the first power generator 110 through the secondswitching device 232.

Since the second inverter 260 has the low-level voltage applied to theinput terminal thereof, it outputs high-level voltage generated byinverting the low-level voltage to the output terminal.

Accordingly, the first switching device 231′ of which the gate electrodeis applied with the high-level voltage is turned off. Therefore, thefirst output terminal OUT1 and the first power generator 110 may beelectrically insulated from each other.

In the case in which the feedback voltage Vfbp is rapidly decreased tothe low-level voltage due to disconnection, short-circuit, or the like,of the feedback wiring 140, the first inverter 250 outputs thehigh-level voltage generated by inverting the low-level feedback voltageVfbp to the output terminal.

Accordingly, the second switching device 232′ of which the gateelectrode is applied with the high-level voltage turned off. Therefore,the feedback terminal FBP and the first power generator 110 may beelectrically insulated from each other.

Since the second inverter 260 has the high-level voltage applied to theinput terminal thereof, it outputs the low-level voltage generated byinverting the high-level voltage to the output terminal.

Accordingly, the second switching device 231′ of which the gateelectrode is applied with the low-level voltage is turned on. Therefore,the voltage Vout1 at the first output terminal OUT1 may be transferredto the first power generator 110 through the first switching device231′. More specifically, the voltage Vout1 at the first output terminalOUT1 may be transferred to the first voltage divider 320 of the firstpower generator 110 through the first switching device 231.

Here, the pull-down transistor 270 may be turned on by the high-levelvoltage output to the output terminal of the first inverter 250.Therefore, the low-level voltage may be stably supplied to the inputterminal of the first inverter 250.

As set forth above, according to certain embodiments of the presentinvention, a DC-DC converter is capable of being normally operatedwithout an additional damage even though the feedback wiring present atan outer portion thereof is disconnected, and an organic light emittingdisplay including the DC-DC converter is provided.

While the present invention has been described in connection withcertain embodiments, it is to be understood that the invention is notlimited to the disclosed embodiments, but, on the contrary, is intendedto cover various modifications and equivalent arrangements includedwithin the spirit and scope of the appended claims, and equivalentsthereof.

What is claimed is:
 1. A direct current (DC)-DC converter, comprising: apower supply unit configured to generate an input power; a first powergenerator configured to: receive the input power from the power supplyunit, receive a selected voltage from a selector and generate a firstvoltage; a first output terminal connected to the first power generatorand configured to output the first voltage; a second power generatorconfigured to receive the input power from the power supply unit, andfurther configured to generate a second voltage; a second outputterminal connected to the second power generator and configured tooutput the second voltage; an external feedback wiring configured toprovide a feedback voltage; a feedback terminal connected to theexternal feedback wiring and configured to input the feedback voltage tothe selector; and the selector connected to the first power generator,and configured to transfer the selected voltage to the first powergenerator, wherein the selected voltage is one of the feedback voltageinput from the feedback terminal and the voltage output from the firstoutput terminal.
 2. The DC-DC converter of claim 1, wherein the selectorincludes: a switching unit including a first switching device and asecond switching device configured to transfer the selected voltage tothe first power generator, wherein the first switching device isconfigured to transfer the voltage output from the first outputterminal, and the second switching device is configured to transfer thefeedback voltage input from the feedback terminal; and a controllercontrolling alternate turn-ons of the first switching device and thesecond switching device.
 3. The DC-DC converter of claim 2, wherein thecontroller includes a comparator configured to compare the feedbackvoltage with a preset reference voltage to determine which of the firstand second switching devices to turn on.
 4. The DC-DC converter of claim3, wherein the comparator turns the second switching device on if thefeedback voltage is larger than the preset reference voltage, and turnsthe first switching device on if the feedback voltage is smaller thanthe preset reference voltage.
 5. The DC-DC converter of claim 2, whereinthe first switching device and the second switching device areimplemented as a transistor; and wherein the controller includes: afirst inverter having an input terminal connected to the feedbackterminal and an output terminal connected to an input terminal of asecond inverter and a gate electrode of the second switching device; andthe second inverter having an input terminal connected to the outputterminal of the first inverter and an output terminal connected to agate electrode of the first switching device.
 6. The DC-DC converter ofclaim 1, wherein the first power generator includes: a first inductorconnected between the power supply unit and a first node; a firsttransistor connected between the first node and a ground power supply; asecond transistor connected between the first node and the first outputterminal; a first switching controller configured to control the firsttransistor and the second transistor; and a first voltage dividerconfigured to divide voltage supplied from the selector to supply thedivided voltage to the switching controller.
 7. The DC-DC converter ofclaim 6, wherein the first voltage divider includes a plurality ofresistors connected in series with each other.
 8. The DC-DC converter ofclaim 1, wherein the second power generator includes: a third transistorconnected between the power supply unit and a second node; a fourthtransistor connected the second node and the second output terminal; asecond inductor connected between the second node and a ground powersupply; a second switching controller configured to control the thirdtransistor and the fourth transistor; and a second voltage dividerconfigured to divide voltage at the output terminal to supply thedivided voltage to the second switching controller.
 9. The DC-DCconverter of claim 8, wherein the second voltage divider includes aplurality of resistors connected in series with each other.
 10. TheDC-DC converter of claim 8, wherein the first voltage has a positivepolarity, and the second voltage has a negative polarity.
 11. An organiclight emitting display comprising: a plurality of pixels connected toscan lines, data lines, a first power line and a second power line; anda DC-DC converter generating a first voltage and a second voltage torespectively supply to the pixels through the first power line and thesecond power line, wherein the DC-DC converter includes: a power supplyunit configured to generate an input power; a first power generatorconfigured to: receive the input power from the power supply unit,receive a selected voltage from a selector, and generate the firstvoltage; a first output terminal connected to the first power generatorand configured to output the first voltage; a second power generatorconfigured to receive the input power from the power supply unit, andfurther configured to generate a second voltage; a second outputterminal connected to the second power generator and configured tooutput the second voltage; and the selector connected to the first powergenerator, and configured to transfer the selected voltage to the firstpower generator, wherein the selected voltage is one of the feedbackvoltage input from the external feedback terminal and the voltage outputfrom the first output terminal.
 12. The organic light emitting displayof claim 11, wherein the selector includes: a switching unit including afirst switching device and a second switching device configured totransfer the selected voltage to the first power generator, wherein thefirst switching device is configured to transfer the voltage output fromthe first output terminal, and the second switching device is configuredto transfer the feedback voltage input from the feedback terminal ; anda controller controlling alternate turn-ons of the first switchingdevice and the second switching device.
 13. The organic light emittingdisplay of claim 12, wherein the controller includes a comparatorconfigured to compare the feedback voltage with a preset referencevoltage to determine which of the first and second switching devices toturn on.
 14. The organic light emitting display of claim 13, wherein thecomparator turns on—the second switching device if the feedback voltageis larger than the preset reference voltage and turns on the firstswitching device if the feedback voltage is smaller than the presetreference voltage.
 15. The organic light emitting display of claim 12,wherein the first switching device and the second switching device areimplemented as a transistor; and wherein the controller includes: afirst inverter having an input terminal connected to the feedbackterminal and an output terminal connected to an input terminal of asecond inverter and a gate electrode of the second switching device; andthe second inverter having an input terminal connected to the outputterminal of the first inverter and an output terminal connected to agate electrode of the first switching device.
 16. The organic lightemitting display of claim 11, wherein the first power generatorincludes: a first inductor connected between the power supply unit and afirst node; a first transistor connected between the first node and aground power supply; a second transistor connected between the firstnode and the first output terminal; a first switching controllerconfigured to control the first transistor and the second transistor;and a first voltage divider configured to divide voltage supplied fromthe selector to supply the divided voltage to the switching controller.17. The organic emitting display of claim 15, wherein the first voltagedivider includes a plurality of resistors connected in series with eachother.
 18. The organic light emitting display of claim 11, wherein thesecond power generator includes: a third transistor connected betweenthe power supply unit and a second node; a fourth transistor connectedthe second node and the second output terminal; a second inductorconnected between the second node and a ground power supply; a secondswitching controller configured to control the third transistor and thefourth transistor; and a second voltage divider configured to dividevoltage at the output terminal to supply the divided voltage to thesecond switching controller.
 19. The organic light emitting display ofclaim 11, wherein the second voltage divider includes a plurality ofresistors connected in series with each other.
 20. The organic lightemitting display of claim 11, wherein the first voltage has a positivepolarity, and the second voltage has a negative polarity.
 21. Theorganic light emitting display of claim 11, further including: a scandriver configured to supply scan signals to pixels through the scanlines; and a data driver configured to supply data signals to pixelsthrough the data lines.